Conveyor control systems have in the past included chains running along the track to which each trolley or vehicle is connected. The speed of the vehicles is constant as is the space between the vehicles. A problem with this type of assembly is that if the chain breaks or one of the vehicles breaks down, the entire system must come to a halt. Therefore, conveyor control systems are using vehicles to have a motor thereon to turn the wheels which receive power from the power rails running along the track. Each vehicle is self propelled so that if one of the vehicles breaks down, the vehicle can be removed without a total disablement of the conveyor system.
One type of an assembly includes self propelled vehicles having a drive motor supplied power via current rails. Included is a rail supplying a command signal which is detected by a vehicle indicative of the speed that the vehicle is to move at. The rail is in isolated sections to present different areas of track with different speeds. The vehicle receives and interprets the command signal and drives the vehicle motor at this requested speed unless external sensors thereon determine the presence of another vehicle or object within its path. Such a system is disclosed in copending application U.S. Ser. No. 028,793 filed Mar. 23, 1987 invented by the inventor herein named and assigned to the assignee of the subject invention. The problem with this type of assembly is that the external command signal needs to be continuously provided, and absolute position along the track where the vehicle moves is unknown.